Fluorescence measuring device for gemstones

ABSTRACT

A gemstone fluorescence measuring device according to the invention generally includes an ultraviolet (“UV”) emission chamber, a UV radiation source, and a light meter assembly. The UV radiation source includes an upper light emitting diode (“LED”) and a lower LED that radiate a gemstone under test from both above and below the gemstone. The UV radiation source provides both trans-radiation and direct radiation to the gemstone, and the UV radiation source has an adjustable intensity, thus facilitating calibration of the fluorescence measuring device. The light meter assembly includes a light detector that detects the visible light emitted from the gemstone under test in response to the UV radiation. The light detector is configured to simulate the spectral characteristics of the human eye. The fluorescence measuring device converts the measured visible light into a numerical lux reading, which can then be converted into a fluorescence grade for the gemstone under test.

FIELD OF THE INVENTION

The present invention relates generally to gemological instrumentation.More particularly, the present invention relates to instrumentation formeasuring the fluorescence of gemstones such as diamonds.

BACKGROUND OF THE INVENTION

Gemstones such as diamonds are traditionally graded based upon theirappearance characteristics. For example, the following diamond qualitiesare typically included in standard grading reports: shape; weight(carat); clarity; color; fluorescence; and cut characteristics. In thecontext of gemstone analysis, “fluorescence” refers to the emission ofvisible light from a gemstone while exposed to ultraviolet (“UV”)radiation. The fluorescence of diamonds is usually graded using thefollowing classifications: None; Faint; Medium; Strong; and Very Strong.

Traditionally, diamonds are graded by human inspectors who have beentrained to identify and quantify the visible characteristics (with orwithout the aid of test equipment). Human inspectors grade thefluorescence of a diamond (and other gems) by illuminating the diamondwith a controlled UV light source and observing the visible lightemitted from the diamond. The human inspectors classify the diamondaccording to the intensity of the emitted visible light. In a diamondgrading lab environment, technicians usually employ fluorescencereference “master stones” to improve consistency. Nevertheless, due tothe inherently subjective nature of human fluorescence grading, somediamonds may be misclassified, especially if the appearance of a diamondis on the borderline between classifications. Furthermore, the samehuman grader may classify a diamond differently depending upon a numberof factors such as: his or her level of fatigue; the environmentalconditions; the size and/or cut of the diamond; the color of thefluorescence; the orientation of the observation; the instability of thelight source; and the like.

The prior art includes a number of instruments designed to “automate”some of the gemstone grading processes by removing the human component.These instruments serve as a confirmation of the human grading process,and are not intended to completely replace the human grading procedure.The prior art, however, does not include an inexpensive, simple tooperate, diamond fluorescence measuring device that is designed toelectronically measure the fluorescence of a diamond by illuminating thediamond with a stable UV light source. In contrast, sophisticated andexpensive fluorescence measuring equipment exists for other uses such asfluorescence spectrophotometry, x-ray, and microscopyapplications—gemstone fluorescence grading does not require suchsophisticated and expensive equipment.

BRIEF SUMMARY OF THE INVENTION

A fluorescence measuring device for gemstones is described herein. Afluorescence measuring device configured in accordance with theinvention employs a stable and adjustable UV radiation or light source.In the example embodiment described herein, the UV source includes twolight emitting diodes (“LEDs”) that are substantially aligned with eachother. A gemstone such as a diamond is positioned between the two LEDs,and the LEDs are activated to provide a combination of trans-radiation(i.e., radiation through the object) and direct radiation (i.e.,radiation toward the object) of the gemstone. The fluorescence measuringdevice includes a light detector or light meter positioned to measurethe visible light emitted from the gemstone. The measured quantity canthen be processed and converted into an alphanumeric grade, a category,or other suitable processing unit.

The above and other aspects of the present invention may be carried outin one form by a fluorescence measuring device for a gemstone undertest. The fluorescence measuring device includes a UV radiation sourceconfigured to provide trans-radiation and direct radiation to thegemstone under test, and a light detector positioned proximate thegemstone under test. The light detector is configured to detect visiblelight emitted from the gemstone under test in reaction to the applied UVradiation.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be derived byreferring to the detailed description and claims when considered inconjunction with the following Figures, wherein like reference numbersrefer to similar elements throughout the Figures.

FIG. 1 is a schematic representation of a fluorescence measuring devicefor gemstones;

FIG. 2 is a diagram that illustrates the geometry of LEDs and a lightdetector of an example fluorescence measuring device;

FIG. 3 is a perspective view of a gemstone pedestal and LEDs of anexample fluorescence measuring device;

FIG. 4 is a perspective view of the gemstone pedestal shown in FIG. 3,and a reflector positioned upon the gemstone pedestal;

FIG. 5 is a front perspective view of a practical embodiment of afluorescence measuring device for gemstones; and

FIG. 6 is a side perspective view of the fluorescence measuring deviceshown in FIG. 5.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention may be described herein in terms of functionalblock components and various processing steps. It should be appreciatedthat such functional blocks may be realized by any number of hardware,software, and/or firmware components configured to perform the specifiedfunctions. For example, the present invention may employ variousintegrated circuit components, e.g., memory elements, digital signalprocessing elements, logic elements, look-up tables, and the like, whichmay carry out a variety of functions under the control of one or moremicroprocessors or other control devices. In addition, those skilled inthe art will appreciate that the present invention may be realized inany number of practical implementations and that the system shown anddescribed herein is merely one exemplary application for the invention.

It should be appreciated that the particular implementations shown anddescribed herein are illustrative of the invention and its best mode andare not intended to otherwise limit the scope of the invention in anyway. Indeed, for the sake of brevity, conventional aspects of UVradiation generation, LED technology, light detection and measurement,gemstone grading techniques, and other features or functions of thesystems (and the individual operating components of the systems) may notbe described in detail herein. Furthermore, the connecting lines shownin the various figures contained herein are intended to representexemplary functional relationships and/or physical couplings between thevarious elements. It should be noted that many alternative or additionalfunctional relationships or physical connections may be present in apractical embodiment.

FIG. 1 is a schematic representation of a gemstone fluorescencemeasuring device 100 configured in accordance with the presentinvention. FIG. 5 is a front perspective view of one practicalembodiment of fluorescence measuring device 100, and FIG. 6 is a sideperspective view of the fluorescence measuring device 100 shown in FIG.5. Fluorescence measuring device 100 is suitably configured to measurethe fluorescence of gemstones, e.g., diamonds. For convenience, thefollowing description of fluorescence measuring device 100 refers to themeasurement and grading of diamonds. The invention, however, is notlimited to diamond applications.

Fluorescence measuring device 100 generally includes an emission chamber102, a UV radiation source 104, a light meter assembly 106, a powersupply 108, and an adjustable current source 110. The example embodimentdepicted in FIGS. 5 and 6 includes a base housing 112 that serves as thefoundation for fluorescence measuring device 100. Base housing 112 canbe formed from metal, plastic, or any suitable material. Base housing112 serves as a housing for power supply circuitry, adjustable currentsource 110, and, if necessary, other circuits, components, and/orfunctional elements of fluorescence measuring device 100 (thesecomponents are hidden from view in FIGS. 5 and 6). Base housing 112 alsoserves as a mounting platform for emission chamber 102 and light meterassembly 106, as illustrated in FIGS. 5 and 6.

One embodiment of fluorescence measuring device 100 receives its powerfrom a standard 120 volt or 240 volt AC line. The example embodimentutilizes an AC/DC adapter (not shown) that converts the AC power into 12volts DC. FIG. 6 depicts an end 114 of the AC/DC adapter attached to asuitable receptacle or plug mounted to base housing 112. In thisembodiment, power supply 108 is realized as the AC/DC adapter. In otherembodiments, power supply 108 may be incorporated into fluorescencemeasuring device 100 itself, e.g., as circuitry located within basehousing 112. As described in more detail below, power supply 108provides power to UV radiation source 104 and, if necessary, to othercomponents of fluorescence measuring device 100. Although not shown,fluorescence measuring device 100 includes a main on/of switch, whichmay be mounted on base housing 112.

Emission chamber 102 is configured to accommodate a diamond under test116. Emission chamber 102 can be formed from metal, plastic, or anysuitable opaque material. In the example embodiment, emission chamber102 is machined from black plastic. Emission chamber 102 includes ahinged access door 118 that covers an access window 120 when closed.When open, access door 118 facilitates the placement and removal of thediamond under test 116. The access window 120 is preferably sized suchthat positioning of the diamond under test 116 can be accomplished usingambient light that enters emission chamber 102. In the exampleembodiment, access window 120 has the following approximate dimensions:1.75 inches by 1.75 inches. When closed, access door 118 “seals”emission chamber 102 and prevents ambient light from entering theinterior of emission chamber 102. After access door 118 is lowered intothe closed position, the force of gravity keeps it in place.

As shown in FIG. 5, fluorescence measuring device 100 may include apedestal 122 located within the interior of emission chamber 102.Pedestal 122 is also depicted in FIGS. 3 and 4. In the exampleembodiment, pedestal 122 is generally cylindrical in shape and itscircumference follows the inner wall contour of emission chamber 102.Pedestal 122 provides a raised level for the positioning of the diamondunder test 116, thus making it easier to insert and remove the diamondfrom the interior of emission chamber 102. The height of pedestal 122 isselected in accordance with the desired radiation and light detectioncharacteristics of fluorescence measuring device 100 (described in moredetail below). In the example embodiment, pedestal 122 is approximately0.05 to 0.10 inches in height. Pedestal 122 also functions as astructural mount for a portion of UV radiation source 104 (in theexample embodiment, a UV LED is mounted within pedestal 122).

In accordance with a practical embodiment, UV radiation source 104comprises a plurality of LEDs. In the preferred embodiment, UV radiationsource 104 includes a lower LED 124 and an upper LED 126. Lower LED 124is centrally mounted within pedestal 122 such that the respective UVradiation is emitted upward. Upper LED 126 is mounted within the upperportion of emission chamber 102 such that the respective UV radiation isemitted downward. The tip of upper LED 126 is shown in FIG. 5, and areceptacle 128 for upper LED 126 is shown in FIG. 6. In operation, theUV radiation emitted from LEDs 124/126 is maintained within emissionchamber 102.

Light meter assembly 106 includes a light detector 130, acontroller-processor 132, and a cable 134 for coupling light detector130 to controller-processor 132. At least a portion of light detector130 is positioned within the interior of emission chamber 102 andproximate the diamond under test 116 (as schematically represented inFIG. 1 and as shown in FIG. 5). In FIG. 5, the portion of light detector130 located within emission chamber 102 is shown at the upper leftcorner of access window 120. As described in more detail below, lightdetector 130 is configured to detect visible light emitted from thediamond under test 116 in reaction to UV radiation applied to thediamond under test 116.

To facilitate accurate fluorescence measurements, the interior ofemission chamber 102, pedestal 122, and other features of fluorescencemeasuring device 100 located within emission chamber 102 havenon-reflective surfaces. For example, the interior of emission chamber102 and pedestal 122 can be coated, anodized, plated, or otherwisecolored flat black to reduce the amount of reflected light detected bylight meter assembly 106.

FIG. 2 is a diagram that illustrates the relative geometry of the LEDs124/126 and light detector 130 of fluorescence measuring device 100. Forpurposes of FIG. 2 and the following description, LEDs 124/126 and lightdetector 130 are depicted as points. In practice, LEDs 124/126 will emitUV radiation from a small area, and light detector 130 will receivevisible light over a small area. The representation of these componentsas points simplifies the description of the geometry.

Upper LED 126 and lower LED 124 share a common emission axis 136(depicted as a vertical dashed line in FIG. 2). In this regard, upperLED 126 emits UV radiation along emission axis 136 toward lower LED 124,and lower LED 124 emits UV radiation along emission axis 136 towardupper LED 126. In other words, the LEDs 124/126 are vertically alignedin the example embodiment. Furthermore, in an actual working embodiment,each of the LEDs emits a relatively narrow, conically shaped, UVradiation beam that forms an angle θ (as shown for LED 126 in FIG. 2).In accordance with one preferred embodiment, the angle θ equalsapproximately 10-20 degrees. This relatively small angle is desirablefor having a maximum reaction in relation to the total produced UVradiation by the LED and because it facilitates initial adjustment andcalibration of the radiation source.

The emission points of LEDs 124/126 are separated by a distance d, asshown in FIG. 2. In the example embodiment, d falls within the range of0.6 to 0.8 inches. The distance d is selected according to the desiredintensity of the visible light emitted from the diamond under test 116.For example, if higher intensity is desired, then the distance d can bereduced. Although the distance d is fixed in the example embodiment, itmay be adjustable to provide an additional degree of freedom tofluorescence measuring device 100.

In the example embodiment, lower LED 124 includes a mounting surface 138(see FIG. 3) configured to accommodate the diamond under test 116. Inthe practical embodiment, lower LED 124 is generally cylindrical inshape with a relatively flat perimeter lip that functions as mountingsurface 138. Optionally, fluorescence measuring device 100 may employ aprotective film or tape between lower LED 124 and the diamond under test116. In operation, the diamond under test 116 is placed onto mountingsurface 138 in a table-down position, as shown in FIG. 1. Accordingly,mounting surface 138 is located between upper LED 126 and lower LED 124.Fluorescence measuring device 100 may alternatively include structure(not shown) for providing a mounting surface distinct from lower LED124. For example, a clear plate or window positioned between LEDs124/126 can be employed.

Referring again to FIG. 2, light detector 130 is preferably located suchthat its “line of sight” 140 to the diamond under test 116 (which, forthe sake of simplicity, corresponds to the position of lower LED 124 inFIG. 2) forms an angle a of approximately 45 degrees with emission axis136. The 45 degree angle simulates the viewing angle commonly used byhuman inspectors when measuring the fluorescence of diamonds.

UV radiation source 104 is configured to provide trans-radiation anddirect radiation to the diamond under test 116. In this context,trans-radiation refers to radiation through the diamond under test 116,while direct radiation refers to radiation on or towards the diamondunder test 116. In the example embodiment, upper LED 126 contributessignificantly to the direct radiation, while lower LED 124 contributessignificantly to the trans-radiation. This combined radiation of thediamond under test 116 results in consistent test conditions, stable UVradiation, and repeatable fluorescence measurements, and allows themeasurement of opaque diamonds or transparent diamonds that react onlysuperficially to UV radiation and do not allow the UV radiation topenetrate substantially into the diamond.

In the practical embodiment, LEDs 124/126 are identical. LEDs 124/126have the following characteristics, which are desirable for use withfluorescence measuring device 100: visible light filtering such that theemitted radiation is pure UV radiation; peak output intensity around 370nm wavelength (i.e., the LEDs provide “long wave” UV radiation); packagediameter equals 5.6 mm. LEDs 124/126 can be realized by the commerciallyavailable LED model number RLT370-10, available from RoithnerLasertechnik of Vienna, Austria. Of course, other commercially availableLED emitters may be suitable for use with fluorescence measuring device100, and LEDs having different operating characteristics can be used tosuit the needs of different practical applications.

Base housing 112 may include indicator or status lights 142corresponding to LEDs 124/126. Status lights 142 indicate whether therespective LEDs 124/126 are in operation. Status lights 142, which maybe driven by power supply 108, monitor the current to each of the LEDs124/126 and indicate failure when they are not lit.

The UV radiation source 104 is adjustable to facilitate calibration andvariation of the amount of UV radiation applied to the diamond undertest 116. In practice, UV radiation source 104 is connected toadjustable current source 110 (see FIG. 1), which regulates the drivecurrent to LEDs 124/126. In turn, the output power of LEDs 124/126,which is dictated by the drive current, is adjusted. In the exampleembodiment, adjustable current source 110 is configured to drive LEDs124/126 from 80% to 120% of their rated power range. Although not arequirement of the invention, adjustable current source 110simultaneously adjusts the current to both LEDs 124/126. Concurrentadjustment is desirable to reduce the complexity of the calibration.Alternate embodiments can have each LED 124/126 independentlyadjustable.

As shown in FIGS. 5 and 6, fluorescence measuring device 100 may employa user interface element 144 (e.g., a rheostat, a potentiometer, one ormore switches, or an electronic controller) for adjusting the outputpower of UV radiation source 104. In this regard, adjustable currentsource 110 can be controlled by user interface element 144.

In the context of this description, the UV radiation source 104, thegemstone mounting surface, and adjustable current source 110 form aradiation subsystem. The radiation subsystem can be employed influorescence measuring device 100 as shown or in other fluorescencemeasuring applications.

Light detector 130 includes a correction filter that converts the actualmeasured values into “human-perceived” values. In other words, lightdetector 130 is configured such that its spectral response simulates thespectral response of the average human eye. In the practical embodiment,light meter assembly 106 is realized as a commercially availablephotographer's light meter device. One device suitable for use as lightmeter assembly 106 is the Mavolux 5032B meter, manufactured by GossenFoto of Nurnberg, Germany. This meter is a very high resolution meter(resolution of 0.01 lux), which is desirable for use in fluorescencemeasuring device 100, where low light intensities are measured. Intypical diamond fluorescence measurements, light intensities fall withinthe range of 0.01 and 5 lux.

Light meter assembly 106 is a battery-powered unit having a power supplythat is independent of power supply 108. Alternate embodiments mayintegrate light meter assembly 106 with fluorescence measuring device100 such that it shares power supply 108.

Controller-processor 132 of light meter assembly 106 includes a display146 and a control panel 148. Display 146 is an LCD element that providesan alphanumeric reading of the visible light measured by light detector130. In operation, display 146 indicates the current light intensity, inlux, measured by light detector 130. Control panel 148 provides a userinterface with buttons that control the on/off status of light meterassembly 106, the display range, the maximum reading, and other featuresrelated to the operation of light meter assembly 106.

Fluorescence measurements using device 100 may be sensitive to the sizeof the diamond under test 116. Ideally, fluorescence characteristics ofa gemstone should be independent of size. The scheme employed byfluorescence measuring device 100—the detection of visible lightintensity within emission chamber 102—may require calibration orcorrection to accommodate the testing of gemstones having a range ofsizes. Furthermore, diamonds with uneven fluorescence can give differentreadings related to the orientation of the diamond on the mountingstage. In this regard, fluorescence measuring device 100 may include areflector 150 configured for placement within emission chamber 102 (seeFIG. 4).

Reflector 150 is formed from a material, such as aluminum, having areflective surface. When placed within emission chamber 102, reflector150 functions to reflect some of the visible light, which wouldotherwise be dissipated within emission chamber 102, toward lightdetector 130. Fluorescence measuring device 100 may include reflectors150 having different shapes, sizes, colors, and other reflectivecharacteristics to accommodate different gemstone sizes and/orfluorescence behaviors. The specific height, thickness, curvatureprofile, radius, and arc length of reflector 150, in addition to thespecific positioning of reflector 150 within emission chamber 102, mayvary depending upon the type of gemstone being tested, the size of thegemstone, the evenness of fluorescence, and the desired calibrationscheme.

As with human fluorescence inspection, master gemstones having knownfluorescence characteristics can be used to calibrate fluorescencemeasuring device 100. In practice, fluorescence measuring device 100should be calibrated at least once a day using one or more mastergemstones. When calibrating fluorescence measuring device 100, the usermay need to tune adjustable current source 110 and/or identify one ormore reflectors 150 for use during actual testing. Of course, thecalibration of fluorescence measuring device 100 can be verifiedperiodically throughout the day. Calibration of fluorescence measuringdevice 100 can compensate for the aging of LEDs 124/126, scratches ordeposits on the emission surfaces of LEDs 124/126, the aging of lightmeter assembly 106, and the like.

Obtaining a fluorescence measurement of a diamond is relativelystraightforward. The access door 118 is opened, and the diamond undertest 116 is placed onto mounting surface 138. In practice, the diamondunder test 116 is placed table-down onto mounting surface 138 andcentered about emission axis 136. Centering is important for consistencyin the measurement and the table-down position is the common methodologyin fluorescence grading of diamonds. Thereafter, access door 118 isclosed and the diamond under test 116 is ready to be radiated. Closureof the access door 118 is a safety measure that prevents UV radiationfrom accidentally escaping from emission chamber 102 and avoidsinfluences of environmental light incorporated into the measurement.

After engaging the main on/off switch, fluorescence measuring device 100should be left to warm up for about five minutes. In addition, theon/off button on light meter assembly 106 is switched to the “on”position. The LEDs 124/126 are activated to provide UV radiation to thediamond under test 116. The entire unit can remain on during an extendedperiod (e.g., throughout a day) because of its low power consumption,limited heat production, and very long lifespan of the LEDs. Asmentioned above, LEDs 124/126 provide both trans-radiation and directradiation to the diamond under test 116. In other words, the diamond isradiated from both above and below. As soon as the light meter has beenactivated, the display 146 should indicate a 0.00 lux reading, as novisible light is recorded in the completely closed emission chamber 102.The light detector 130 detects the visible light emitted from thediamond under test 116 in reaction to the UV radiation. As mentionedabove, when excited by UV radiation, certain gemstones fluoresce withvisible light. The quantity detected by light detector 130 is processedand converted into a numerical lux reading, which is then rendered ondisplay 146. The lux reading can be recorded by hand or recordedelectronically for computer storage and/or processing.

The numerical lux reading for the diamond under test 116 can beconverted into a diamond fluorescence grade using any number offluorescence grading scales recognized in the diamond trade. Thus, thefluorescence of the diamond under test 116 is graded based upon thedetected visible light measurement captured by light meter assembly 106.As one practical example, see the following scale, where the measuredlux values are representative of a typical application: Measured LuxFluorescence Grade 0.04 or less None 0.05 to 0.14 Faint 0.15 to 0.44Medium 0.45 to 1.34 Strong greater than 1.35 Very StrongTherefore, fluorescence measuring device 100 can be used to verify thefluorescence grade of a human diamond inspector or to independentlygrade the fluorescence of a diamond. Fluorescence measuring device 100removes the human component while simulating the human observationconditions traditionally associated with fluorescence grading.

The present invention has been described above with reference to apreferred embodiment. However, those skilled in the art having read thisdisclosure will recognize that changes and modifications may be made tothe preferred embodiment without departing from the scope of the presentinvention. These and other changes or modifications are intended to beincluded within the scope of the present invention, as expressed in thefollowing claims. 12

1. A fluorescence measuring device for a gemstone, said fluorescencemeasuring device comprising: an ultraviolet (“UV”) radiation sourceconfigured to provide multi-directional radiation to the gemstone; and alight detector positioned proximate the gemstone, said light detectorbeing configured to detect visible light emitted from the gemstone inreaction to UV radiation applied to the gemstone.
 2. A fluorescencemeasuring device according to claim 1, wherein said UV radiation sourcecomprises a plurality of light emitting diodes (“LEDS”).
 3. Afluorescence measuring device according to claim 2, further comprising auser interface element for adjusting the output power of said LEDS. 4-6.(canceled)
 7. A fluorescence measurement method for gemstones, saidmethod comprising: radiating a gemstone with multi-directionalultraviolet (“UV”) radiation; detecting visible light emitted from thegemstone in reaction to UV radiation applied to the gemstone, resultingin a detected visible light reading; and grading fluorescence of thegemstone based upon the detected visible light reading.
 8. A methodaccording to claim 7, wherein said radiating step radiates the gemstonewith a UV radiation source in a closed emission chamber that hassubstantially no visible light except for the visible light emitted fromthe gemstone in reaction to UV radiation. 9-10. (canceled)